feat(parser): add readonly property unset protection

- Check for readonly property when calling unset on object properties
- Throw fatal error when attempting to unset readonly properties
- Add proper error message with property display name
- Include tests for unset operations on readonly properties
- Support both regular readonly properties and readonly class properties
- Ensure consistent error handling for readonly property access violations

phpunit/code/unset-readonly-class-property.php

@@ -0,0 +1,16 @@
+<?php
+
+readonly class ReadonlyClassPropertyUnset
+{
+    public int $value;
+
+    public function __construct()
+    {
+        $this->value = 1;
+    }
+
+    public function clear(): void
+    {
+        unset($this->value);
+    }
+}

phpunit/code/unset-readonly-property.php

@@ -0,0 +1,17 @@
+<?php
+
+class ReadonlyPropertyUnset
+{
+    public readonly int $value;
+
+    public function __construct()
+    {
+        $this->value = 1;
+    }
+}
+
+function main(): void
+{
+    $object = new ReadonlyPropertyUnset();
+    unset($object->value);
+}

phpunit/src/UndefineTest.php

@@ -18,6 +18,19 @@ class UndefineTest extends \BaseTest
         $this->exec('Attempt to unset static property', 'unset-static-prop.php');
     }
 
+    public function testUnsetReadonlyPropertyIsRejected(): void
+    {
+        $this->exec('Cannot unset readonly property `ReadonlyPropertyUnset::$value`', 'unset-readonly-property.php');
+    }
+
+    public function testUnsetReadonlyClassPropertyIsRejected(): void
+    {
+        $this->exec(
+            'Cannot unset readonly property `ReadonlyClassPropertyUnset::$value`',
+            'unset-readonly-class-property.php'
+        );
+    }
+
     public function testPropertyAccessOnUndefinedVar(): void
     {
         $this->compile('undefined-prop-access.php');

src/Parser/PropertyAccessTrait.php

@@ -737,6 +737,14 @@ trait PropertyAccessTrait
                     $propertyId = $this->getPropertyIdentifier($var, $var->var, $var->name);
                     $def = $this->getNativePropertyDef($var);
                     if ($def) {
+                        if ($def->isReadonly()) {
+                            $this->fatalError(
+                                $var,
+                                'Cannot unset readonly property `'
+                                . $this->getObjectPropertyTypeCheckDisplayName($var)
+                                . '`'
+                            );
+                        }
                         // Object typed properties are backed by Zend object
                         // properties, so PHP can represent their uninitialized
                         // state after unset(). Keep that behavior instead of